In the last decades, the marketplace has focused on wireless networks, making wireless networks grow rapidly. Different technologies have been developed on a global as well as a local level. Most of these technologies depend on a centralized hierarchical fixed infrastructure, which limits both survivability and scalability, and is dependent on the pre-configuration of the network. In addition, the cost of this expensive infrastructure is a major consideration.
Recently, infrastructureless networks (known as Mobile Ad-hoc Networks (MANETs)) have been developed as a means of addressing the needs for a more flexible, durable and cost efficient network system than conventional centralized hierarchical fixed infrastructure systems offer. Nodes in MANETs can be mobile or fixed routers and can be connected by wired or wireless links using one or more different technologies. These Nodes function as routers by discovering and maintaining routes to other Nodes in the network. In contrast with infrastructured networks, in MANETs there is no need for centralized infrastructures, such as base stations or pre-configured routers (i.e., network elements). This distributed characteristic allows the system to be more durable and more scalable. MANETs are often fast, self-built, self-configured, and adaptive to dynamic changes. MANETs are useful in a large number of applications, making them particularly useful when there is no network infrastructure or such infrastructure has been destroyed. It is clear that MANETs will play a very important role in the continued development of the computing and telecommunication market.
MANETs have several characteristics. These networks have highly dynamic topology. Most of the MANETs Nodes are mobile Nodes. These Nodes move rapidly and freely. Because of this mobility, the network topology changes rapidly and unpredictably. As opposed to fixed links, MANET links, which are wireless links, have limited and variable bandwidth, higher power consumption, limited energy and higher bit error rate. In addition, these links might be bi-directional or unidirectional. A large number of the Nodes in MANETs are mobile, and most of them depend on their batteries' energy, which is limited. Hence, energy conservation and fair distribution of energy usage should be taken into consideration.
In any network, the goal of the routing algorithm is to build routes from the sources to the destinations to be used by the data. These routes should maximize network performance. To solve the routing problem in MANETs, the goal of the routing algorithm should be achieved, while taking into consideration the special network characteristics. The routing algorithm should deal with the rapid changes in the network and it should optimize more than one parameter of the quality of service parameters (QOS) in the network, such as Node energy, link bandwidth, end to end delay, queuing delay, number of hops, links' signal to noise ratio, error rate, etc.
Many routing algorithms have been developed for MANETs; these algorithms can be classified into two groups. The first group is called table driven routing algorithms (such as DSDV, CGSR, GSR, FSR, HSR, WRP, etc.). See Elizabeth Royer and C-K Toh, “A Review of Current Routing Protocols for Ad-Hoc Mobile Wireless Networks”, IEEE Personal Communications Magazine, April 1999, pp. 46-55, P. Misra, “Routing Protocols for Ad Hoc Mobile Wireless Networks”, (adhoc_routing.pdf). [Online]. Available: http://www.cis.ohio-state.edu/˜jain/cis788-99/adhoc_routing/index.html, and C. E. Perkins and P. Bhagwat, “Highly Dynamic Destination Sequenced Distance Vector Routing (DSDV) for Mobile Computers,” Computer Communications Review, pp. 234-244, October 1994. These algorithms need frequent updating for the routing tables, which increases the routing overheads.
The second group is called source initiated on demand routing algorithms (such as AODV, DSR, TORA, ABR, SSR, etc.). Most algorithms of this class depend on flooding to find the route from sources to destinations, which increase the routing overheads. See Elizabeth Royer and C-K Toh, “A Review of Current Routing Protocols for Ad-Hoc Mobile Wireless Networks”, IEEE Personal Communications Magazine, April 1999, pp.46-55, P. Misra, “Routing Protocols for Ad Hoc Mobile Wireless Networks”, (adhoc_routing.pdf). [Online]. Available: http://www.cis.ohio-state.edu/˜jain/cis788-99/adhoc_routing/index.html, and Charles E. Perkins and Elizabeth Royer “Ad-hoc On-Demand Distance Vector Routing.”, Proceedings of the 2nd IEEE Workshop on Mobile Computing Systems and Applications, New Orleans, La., February 1999, pp. 90-100.
Most MANETs routing algorithms need a large number of routing packets to maintain routes from sources to destinations. This large routing overhead affects the scalability of the network. This large routing overhead affects the network performance because it uses a significant part of the wireless bandwidth and of the Node's energy. In addition, most of these algorithms are optimizing only one parameter, which is in most cases the number of hops. These algorithms maintain only limited number of routes, which affect the survivability of the network. Therefore, a need exists of a routing method which will solve the routing problems in MANETs and obtain high performance, adaptive, reliable and survivable network.